The use of metal phosphides and metal disulfides such as PtP.sub.2, Ni.sub.2 P and Co.sub.2 P as electrocatalysts in electrochemical cells, especially in fuel cells with alkaline electrolyte, is already known (U.S. Pat. Nos. 3,411,953; 3,449,169; 3,451,852 and 3,573,988). However, these catalysts are still unsatisfactory in various respects. The use of expensive metals such as platinum in PtP.sub.2 runs counter to the economical application of electrochemical cells like fuel cells. Beyond this, the natural occurrence of platinum is limited. On the other hand, there is a great need for catalysts which can be used in electrochemical cells with acid electrolyte, and in them, as again, catalysts for the anode. In addition, the catalysts should have a wide spectrum of applicability. Tests have shown, for example, that nickel and cobalt phosphide (Ni.sub.2 P and Co.sub.2 P), known for the anodic oxidation of hydrazine, corrodes and is, therefore, not suited for the oxidation of hydrogen in fuel cells with acid electrolyte.
Also, metal phosphide catalysts for electrodes, particularly anodes, of electrochemical cells, particularly fuel cells with acid electrolyte, have already been proposed, containing at least one metal phosphide of one or more metals of the first and seventh side group as well as the metals of the iron group of the periodic table of elements with a phosphorus content in the metal phosphide of at least 1 phosphorus atom per metal atom, (U.S. patent application Ser. No. 343,959 filed Mar. 22, 1973). These electrocatalysts containing metal phosphides rich in phosphorus have proven to be suitable for the electrochemical oxidation of hydrogen. High current densities can be obtained with electrodes containing such catalysts. One electrocatalyst from this series is cobalt phosphide CoP.sub.3, for example. It has also been found that arsenic can be substituted for phosphorus in these compounds and that such compounds, such as the compound CoAs.sub.2, are also catalytically active. It is an unfavorable factor, however, that the corrosion resistance range of the said compounds is relatively narrow, amounting to only about 150 mV for CoP.sub.3, for example, when measured against the potential of the reversible hydrogen electrode.
It is an object of the invention to provide a new group of electrocatalysts, i.e. catalysts for electrodes of electrochemical cells, by which the supply of effective electrocatalysts can be enlarged considerably. Specifically, it is an object to provide new electrocatalysts which enable a greater selection of active anode materials, a special application being fuel elements with acid electrolyte. It is a further object of the invention to provide a new electrocatalyst which is inexpensive and maintains a high catalytic efficiency for a long period of time, i.e. it is indifferent to catalyst poisons. It is a further object of the present invention to provide a new electrocatalyst that is relatively resistant to corrosion.